The present invention relates to an endoscope optics fitted with lens elements and having a securing device to secure the position of the lens elements against shifting on account of impacts.
Such endoscope optics are used, in particular, in medical endoscopes. They comprise a configuration of several lens elements, typically a set of rod lenses acting as optical relays and a set of objective lens elements at the distal ends of the rod lenses. The set of objective lens elements are typically provided together with the rod lenses as an integrated unit. Herein xe2x80x9crod lensxe2x80x9d denotes a thick, cylindrical lens fitted with its optical surfaces at each rod end and transmitting the images axially. An ocular, typically mounted apart from the set of rod lenses, is mounted at the proximal end of this set. The rod lens elements and the objective lens elements typically are mounted inside a system tube. The system tube aligns the lens elements and is hermetically sealed, for instance by means of windows, as required in steam sterilization in medical applications.
Such an endoscope should be highly flexible in order to permit insertion in an easily bent manner into the body ducts. The sensitive rod lenses must be protected against breaking. Typically, radial play is provided when mounting the lens elements in a system tube in order that the elements do not break when the tube is being bent.
The lens elements must be secured in their mutual configuration to assure good endoscopic optic quality. In other words, the lens elements must be affixed to each other at axially defined spacings and they must also be radially fixed. Securing devices for such purpose are known. Conventionally, the lens elements rest radially against the system tube and are axially spaced apart by spacer stubs mounted between them.
In case of impact on the endoscope optics, for instance if the endoscope falls from a table onto the floor, the lens elements may shift on account of the deceleration forces they experience. In the process, the lens elements may tip, which would entail shifting the optics direction of viewing. However, the lens elements may also rotate, with the same result, because most mass-produced rod lenses exhibit a deviation between the optic and geometric axes.
A securing device is required to prevent such effects. One such securing device is known from the post-published German patent application 19,742,454.6-51. In this design the rod lenses are mounted in a stable position and at a controlled oblique position using tubular spacers. The rod lenses in this design will always return to the stable position even after having undergone impacts. However, this securing device does not adequately prevent rotation of the lens elements it holds.
A design disclosed in the German patent document 39 12 720 C2 replaces the system tube by a shrink tube. The shrink tube is larger than required before shrinkage in order to permit easy insertion of the lens elements therein. After shrinkage, the shrink tube secures the lens elements by firmly locking them radially. As a result, the lens elements are permanently well configured one with another and, furthermore, they are secured against rotation. However, this design incurs the drawback of the cumbersome shrinkage process and of the need to use specific shrinking plastics, which exhibit other material properties that are interfering. Also, such an optics assembly cannot be subsequently repaired but can only be exchanged as a whole. Moreover, the shrinkage material used is heat sensitive and generally not appropriate for steam sterilization. Most of all, permanent securing of the lens elements is not assured by this material because of material tolerances, manufacturing tolerances or the effects of subsequent thermal influences. If the materials affixing force drops somewhat, the lens elements will become loose and can be shifted.
The objective of the present invention is to fit an endoscope optics of the aforementioned type with a securing device, wherein the securing device is easily installed, repairable, and permanently secures the lens elements.
The present invention is based on the insight that the impact-resistance of the optics can be assured already by holding the ends of the lens elements mutually aligned and non-rotatable at each abutment surface. This goal is reached in the present invention using a tube that is present at least at one abutment surface. The tube is widened at an end from a diameter less than that of the rod lenses. The tube will elastically and permanently grip the ends of the lens elements. The tube may be housed, with play, in the system tube to assure that the optics are rupture-safe when being bent. Such a tube is able to yield slightly in a resilient or elastic manner in the case of impacts, thus saving the components from rupture. The tube will also allow thermal expansions of the lens elements, while nevertheless keeping them mutually axially aligned and non-rotatable. When the tube is widened, the lens elements are easily installed or easily exchanged for repairs. The tube mutually securing the lens elements in this manner keeps an assembly together and, as a result, the pairs of lens elements or the full lens of the endoscope optics can be handled as one unit. For instance, the pairs of lens elements or the entire endoscope optics can be inserted into a system tube or another installation site. Because the radially resilient securing device also retains axially, tubular spacers securing the axial spacing between the lens elements may be eliminated.
A securing tube can mutually secure two lens elements at their joint or interface to assure their essential optical alignment. However, in accordance with other aspects of the present invention, the tube may also run completely across the secured lens elements to protect them even better against mutual tilting.
In further accordance with the present invention, the tube advantageously assumes the form of a hose made of a circumferentially elastic material, for instance an elastomer or the like. Such a hose must be circumferentially widened to allow insertion of the stack of lens elements. Insertion may be facilitated, by using compressed air to pressurize the inside of the hose or, advantageously, by externally applying a vacuum to the hose.
Alternatively, and according to other aspects of the present invention, the tube may be in the form of a pullover stocking such as is illustratively known form the German patent document 19 630 666 A1. Such a pullover stocking can be manufactured in its narrow mode. In this case, the stocking must be widened by axial pressure to install the lens elements. After being released, the stocking resumes its narrow configuration and wraps the lens elements again.
In another embodiment, the stocking also may be manufactured in the wide mode. In this case, following insertion of the lens elements the stocking may be axially tensioned in order to tightly enclose the lens elements. The stocking would thereafter require tensioning to maintain in its final assembly position.
Alternatively, the tube includes a longitudinal slot and is made of a flexurally elastic material. The tube is widened at the slot to permit insertion of the stack of lens elements. After being released, the tube will elastically close around the lens elements.
In accordance with other features of the invention, the tube is formed as a strip coil. Such a strip coil offers enormous cost advantages. Moreover, a strip coil offers substantial installation advantages. A strip coil normally in a narrow configuration can be widened, to permit insertion of the lens elements, by seizing and oppositely rotating the ends of the strip coil. Upon being released, the coil encloses the elements in a radially inward resilient manner with excellent securing efficacy. In its advantageous metallic embodiment, the coil is exceedingly well suited for long life under autoclaving. Another essential advantage offered by the strip coil is that, following rotational widening and release, the restoring force is not only radial but also in the longitudinal direction. Accordingly the coil not only secures the lens elements against tipping and rotation, but also assures their axially resilient support, without need for a separate device. If, in this manner, the stack of lens elements is axially prestressed, then special means, for instance the conventional tubular spacers, will be required to secure the axial gaps between the lens elements.
The tubes of some embodiments of the present invention may consist of flexural materials such as plastics. However, these tubes may alternatively and advantageously be made of a metal such as spring steel. The metal design is highly reliable under heat (for instance autoclaving) and also offers long life.
In accordance with other features of the invention, a slotted tube may be advantageously provided with a slot running parallel to the tube axis. This design offers simplicity, the slot being opened using simple means to insert the lens elements.
Such a slot can be very narrow and, as a result, the tube in its securing mode will almost entirely enclose the lens elements. However, a very wide slot, that is one for which the tube encloses the lens elements only slightly more than 180xc2x0 still assures that the securing tube will hold the elements while also allowing, by opening the slot slightly more, to insert the lens elements sideways. Accordingly, the elements need not be inserted from the tube ends as they are in conventional assembly. The wide-open slot moreover allows accurately adjusting the elements by a simple, lateral intervention into the tube, both in the axial and in the rotational direction. Such adjustment, for instance, permits optimal matching of the lens elements to each other wherein the optic and geometric axes do not coincide.
As already mentioned above, the tube of the invention might couple every two lens elements only at abutment surfaces or individual sets of lens elements. In accordance with further features of the present invention, all the lens elements of the endoscope optics can be mounted, aligned and secured in one tube. Provided that the tube is appropriately designed, for instance as a continuous longitudinally slotted, dimensionally stable tube, the elements can be processed further.
The securing tube according to the present invention may secure mutually the lens elements of a multi-element lens, or also the objective lens, relative to the adjoining rod lens. When configuring all the lens elements of the endoscope optics in one tube, the objectives lens elements also are advantageously aligned and secured within the same configuration.
When the endoscope optics are fitted with a system tube, the circumferentially expansible tube of the invention secures the lens elements against axial and/or radial shifts, in particular when being subjected to impacts, and the assembled tube rests directly in resilient manner against the lens elements. To avert flexurally loading the lens elements when bending the system tube, a radial play is provided such that some bending of the system tube is feasible without thereby stressing the lens elements to rupture.